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Hi
Just installed my legato 3 and noticed after a few tracks, during an intermission, that SE output has a crackling and fizzing on both channels. I seem to remember from Legato 2 this could be related to the 1/2 watt resistors? Anything I can check?
I get no crackling on balanced output, although I am getting occasional rustling and pops - can I assume that that is dc offset drift and that I really ought to have caps in place?
Cheers
James
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When in doubt, use AC coupling caps on the balanced outputs.
No, it would not be the resistors. They are not even close to being stressed.
Good quality pics might help spot the problem, but try AC coupling first.
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Thanks Russ. I'll try and eradicate the crackling on SE outputs first, then check balanced out again.
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Update on this. I've replaced the 1W resistors with the takmans I had on legato 1. No change. Also removed the opamp socket and soldered opamp to board. Also no change. Touched up all solder joints.
So, I have music playing (very nicely too), but have crackling going on in the background on SE. It's prominent enough in the right channel to hear from listening position with no music playing (I am nearfield though...). Left channel is quieter, but there. Any thoughts at what to look at?
I've cap coupled balanced output, but it doesn't sound as good to me as SE. Cap rolling will eventually be done - wima mks2-xl in there at the moment. Balanced had some rustling/wind type noise on the right channel as well at switch on, but then went quiet. I left it with no music playing for some time and everything was quiet. Maybe a slight bit of hum in left channel.
If it'll help I'll get some photos done next time the board is out.
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Try driving just headphones alone or another amp and see if there is a change. There is no reason the Legato itself should cause this. Edited by user Wednesday, June 8, 2011 7:31:47 AM(UTC)
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Rank: Advanced Member
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Thanks Russ. Is it feasible there's a dodgy component somewhere on the board? Having said that, it's on both channels.
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Some photos. The underside looks remarkably messy actually. Doesn't look as bad in the flesh! Very spitty solder I have here at the moment.  
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It could very well be the metal can op-amp you are using. I have heard of several people having stability issues with them.
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I should add, it was the same with the plastic opamp as well, the metal can was whacked in to test. No change.
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Ok well next test is to test it in isolation by simply driving some SE headphones directly.
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Did you mount the buffers?
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Ha, no, they were premounted, I just added some more solder when touching up the other joints. Spade sized iron and spitty solder doesn't help matters. In the meantime, ivy is sounding rather nice! I have a phones socket on order so will test that when I get the chance. Cheers, James PS: As messy as things are starting to look, the fundamental characteristics of the noise haven't changed at all. It's a very transistory kind of buzz. I'll try the phones before any more desoldering takes place... Edited by user Wednesday, June 8, 2011 11:39:36 AM(UTC)
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Just to know, did you adjust your DC offset correctly?
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Yup, both SE and balanced reading zero (or as near as I could get, within a few points of mV).
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Test with headphones but also I would recommend you clean the entire surface to make sure there is no lead bead that makes contact where it shouldn't.
take a look at the power input jacks. There seem to be some left over solder.
Ciao!
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Thanks. Any recommendations on what to clean the surface with?
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LeonvB wrote:Isopropyl alcohol and an old toothbrush.
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I would clean up the whole board with a strip that absorbs solder and resolder with something proper
hot iron working fast
imo
Leif
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Ok, I've cleaned the board, desoldered and resoldered some of the connections. SE Left channel is now very quiet - there's a faint buzz from the tweeter with my ear right up to it. Right channel still has a prominent buzz, although the low level hum that was there has gone. So I'll have to give that channel some more attention. Cheers for all the help so far.
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